1. Field of the Invention
The present invention is directed to a method for preparing decentralized redundant units in a communication system to be put in service ("commissioning" the system).
2. Description of the Prior Art
The offering of new performance features and services has led in recent years to an increase in the degree of complexity of contemporary communication systems. This means that a communication system is constructed of a number of subscriber stations (terminals) with procedures that control these stations. These procedures, collaborating with one another, control the communication flow and the respectively requested services. The processing and control of the pending tasks in contemporary communication systems is achieved by a decentralization of executive activities. This means that programs and data that were stored in the central control means in earlier systems and were executed therein have been displaced to the peripheral units and pending tasks are processed at the peripheral units independently of the central control means. In particular, this has the advantage that even an outage of the central control means need not necessarily lead to a total restriction of the communication traffic. The programs and data relating to the peripheral units must, however, be transmitted from an external storage medium to those peripheral units in preparation for placing the communication system in service and must be stored at the peripheral units. This requirement is likewise present after an outage or, respectively, partial outage, of the communication system, or even in the case of an expansion with new peripheral equipment.
For preparation prior to placing the system in service, the peripheral units are loaded with program information (switching-oriented, operation and maintenance and administrative programs) by the central control means and are also loaded with the data associated with the peripheral units (i.e. data identifying equipment location, signaling, authorizations, call numbers, individual characteristics of trunk lines and subscriber line circuits, as well as data with respect to the expansion state and the configuration of the peripheral equipment). The program sets and data sets to be loaded into the peripheral units are substantial and exhibit significant growth as a result of the trend to more and more high-capacity communication systems.
As a consequence of the size of the data sets as well as the large number of programs, however, the loading processes from the external storage medium into the peripheral units require an extremely long time. Since contemporary communication systems are being constantly expanded by new services and performance features, and thus the programs and data which control these systems are also becoming more and more extensive, increasing significance is accorded to the reduction of the loading times. Since other demands related to dependability are generally made of a communication system than are made of many other technical systems and installations such as, for example, data processing systems, the loading events must be executed as quickly as possible so that the communication system is optimally available at any time to all subscribers within the scope of its capacities, a demand that is also made of communication systems by CCITT and Bellcore. This demand is taken into consideration, in particular, not only on the basis of the redundant nature of the central control means and message distribution (buffer) units, but also by the redundancy of the peripheral units themselves. The switching-oriented availability of the communication system is not present or is greatly limited during the loading of the peripheral units or a portion of the peripheral units with program or data information. This requires an optimally fast start, and thus an optimally fast loading of the peripheral units in restart situations for example, after software errors (Bellcore Requirements TR-TSY-509, TR-TSY-512, TA-TSY-284, TA-TSY-1047, CCITT Q.700, Q.706, Q.725). The loading times themselves are primarily limited by the transmission rate of the communication system in the direction to the peripheral units and also by the performance of the central control means in offering the loading information and by the transmission performance at the interface between the central control means and the message distribution units. Since, in case of a malfunction, one half of a redundant peripheral unit must assume the work of the down half without a significant loss of stable connections (Bellcore Requirement permitting a maximum of 64 connections), program and data information are loaded into both halves of the peripheral unit within the format of the start up. Data updatings of the respective halves ensue during operation, for which a synchronous connection is provided between the two halves of the peripheral unit.
European Patent 0 294 644 discloses a method for the transmission of data and programs into the peripheral units of a communication system. In that method programs and data are transmitted into the peripheral units in two transmission processes (stages). The first transmission process is implemented before the beginning of the switching-oriented operational execution, whereas the second transmission process is implemented after the beginning of the switching-oriented operational execution. Subscriber-associated data are reloaded as needed particularly during the second transmission process. A modification of this method in view of the first transmission process for the case of redundant peripheral equipment provided with a synchronous connection is shown in FIG. 1 herein.
As shown in FIG. 1, an external storage medium as well as a central control unit therein are connected via two trunk lines to a pair of redundant message distribution (buffer) units which undertake the error-protected transmission of the loading messages as well as the normal switching-oriented and operation and maintenance control messages. These are in turn connected via further trunk lines to redundant peripheral units arranged in pairs, whereby both message distribution units of the pair are connected to both peripheral units. The peripheral units in each pair of peripheral units are also connected to one another via a synchronous line. The loading of programs and data from the external storage medium to the peripheral units occurs such that all programs and data are first divided into a plurality of parts. Subsequently, a transmission is then implemented via both trunk lines to the respective message distribution units connected thereto. From these latter units, the transmission of the respective parts of the data and programs to the peripheral units a pair to be loaded then ensues. Ultimately, all of the programs and data relating to the peripheral units are completely stored in each unit of each pair of redundant peripheral units after the loading event. Updated data are transmitted between both peripheral units in a pair during the switching-oriented operation via the synchronous connection, so that a switch can be immediately undertaken given outage of one peripheral unit to the redundant peripheral unit in the pair and this latter unit can assume the switching-oriented communication traffic without delay and optimally loss-free on the basis of its updated data.
A problem associated with this known procedure is that the entire program controlling the peripheral units as well as all data connected therewith, particularly base loading data, must be loaded into each peripheral unit of each pair of redundantly peripheral units within the format of the first transmission process, using both message distribution units. The message distribution units that determine the loading time are thus in fact fully used however, they redundantly transmit the loading information into a pair of redundant peripheral units. This problem acquires a further dimension when one takes the fact into consideration that a specific task is assigned to each peripheral unit. Thus, for example, specific peripheral units are exclusively responsible for the transmission of the data that are sent from other communication systems (trunk line unit), whereas other peripheral units exclusively process data from subscriber terminal equipment (subscriber line unit). In this respect, the problem thus arises in this known system that different complete programs must be loaded into different subsets of the pairs of peripheral units. This occurs by multiple, successive execution of the aforementioned sequences or by forming a complete program that covers all associated programs of a given type.